As a method for imparting water/oil repellency to the surface of an article (such as a fiber product), a method of treating the article by means of a water/oil repellent composition composed of an emulsion having, dispersed in an aqueous medium, a copolymer having structural units based on a monomer having a polyfluoroalkyl group (a polyfluoroalkyl group will be hereinafter referred to as a Rf group) having at least 8 carbon atoms, has been known.
However, recently, EPA (US Environmental Protection Agency) has pointed out that a compound having a perfluoroalkyl group (a perfluoroalkyl group will be hereinafter referred to as a RF group) having at least 7 carbon atoms is likely to be decomposed in the environment or in the body, and the decomposition product is likely to be accumulated, i.e. it presents a high environmental impact. Therefore, a water/oil repellent composition comprising a copolymer which has structural units based on a monomer having a RF group having at most 6 carbon atoms, and has no structural units based on a monomer having a RF group having at least 7 carbon atoms, has been required.
As a water/oil repellent composition containing such a copolymer, the following water/oil repellent composition has been, for example, proposed (Patent Document 1).
A water/oil repellent composition comprising a copolymer having structural units based on the following monomer (a), structural units based on the following monomer (b) and structural units based on the following monomer (c), and an aqueous medium, in a molar ratio of structural units based on the monomer (b) to structural units based on the monomer (c) ((b)/(c)) of at least 1:
Monomer (a): A monomer having a RF group having at most 6 carbon atoms.
Monomer (b): Vinyl Chloride.
Monomer (c): A vinyl ether having no polyfluoroalkyl group and having a crosslinkable functional group.
An article having its surface treated with the water/oil repellent composition has favorable water repellency after drying without forcibly heating after washing (hereinafter referred to as washing durability). Here, on an article (a fiber product such as a sports wear) having its surface treated with the water/oil repellent composition, a moisture-permeable waterproofing film is provided on the rear side so as to impart a function to release water vapor by sweating from the body and a function to shut out the rain (Patent Document 2). As a method for producing such an article having a moisture-permeable waterproofing film, a lamination method or a coating method is well known.
The lamination method is a method of bonding a porous polyfluoroethylene film or a microporous polyurethane resin film to the rear side of an article treated with a water/oil repellent composition by means of e.g. an adhesive component. The coating method is a method of coating the rear side of an article treated with a water/oil repellent composition, with a coating liquid containing a polyurethane resin, an acrylic resin or the like. This article is required such that the resin film bonded or coated is not easily separated.
Further, as a medium contained in the coating liquid, in the case of dry coating of forming a resin film by drying after coating, it has been known to use a highly volatile solvent such as methyl ethyl ketone, ethyl acetate, toluene or isopropyl alcohol. On the other hand, in the case of wet coating of forming a resin film by coagulation in water, a polar organic solvent such as N,N-dimethylformamide (hereinafter referred to as DMF) is used.
However, since a moisture-permeable waterproofing film is formed on the rear side of an article treated with the water/oil repellent composition, if a coating liquid is applied, the coating liquid infiltrates into the surface of the article, and a resin film is formed even on the surface side of the article, and thus the design of the article may be impaired.